inexpensive, easy to find alarms that rely on ionization technology. they work well to detect fires with fast flames, but experts say they may not save i in smoldering smoky fires that can strike while you sleep. don russell is a scientist at texas a&m. when i buy a smoke detector, i assume they're going to sound when there's smoke. >> that's a reasonable assumption, but it's wrong. >> reporter: we had him set up a test, playing thee ionization detectors in a room, then setting a couch on fire. toxic smoke is building, but it takes 36 minutes for the first detector to go off. but there's another technology out there that gives you better warning in these fires. it's called a photo electric detector. so dr. russell set up another test. this time with a photo electric next to those three ionization detectors. 17 minutes in, with barely any smoke in the room, the photo electric sounds the alarm. the ionizations? they're still silent for another 21 minutes. even with smoke everywhere. >> if i would have relied on ionization, then my family probably wouldn'